Synthetic wall coatings for new construction and renovation generally utilize the application of a synthetic coating to the exterior of a building which is easily applied and manipulated to produce an attractive outer surface. A synthetic stucco composition which is trowel applied is particularly preferred to produce a decorative wall coating of a desired texture. Such a synthetic stucco material is generally used in energy saving composite wall systems or may be used as a finish over existing masonry walls. Such stucco-type compositions usually include a latex binder combined with various fillers and additives such as pigments. Such stucco coatings may be used to insulate and waterproof, as well as to decorate, the exterior of buildings.
Generally, silica sand is used as the filler, comprising up to 60% of the stucco composition. Such silica usually includes a trace amount of tramp iron which, over time, bleeds through the applied coating, causing streaks or discoloration. In addition, silica sand is heavy, adding substantial weight to the compositions, increasing transportation costs and adding to the fatigue of workers who must add and work the composition on a wall with a trowel. The silica sand is also of non uniform size and shape, producing a non-uniform surface texture easily susceptible to cracking. A cratered surface is common, even after manipulation with a trowel.
In U.S. Pat. No. 4,391,647 to Deer et al, a spackling joint compound is disclosed for use as a stucco composition. The compound includes a proportion of hollow silica particles which have an average diameter of from about 25 microns to about 100 microns, and a density of from about 0.1 gm per cc to about 0.2 gm per cc. About one to five parts by weight of hollow-silica particles are added to a base composition. The use of hollow-silica particles is said to produce a lighter weight composition and provide less trowel drag during application, with improved surface leveling characteristics.
In U.S. Pat. No. 4,171,228 to Lowrey, a pigment composition for a high build protective coating is disclosed which includes pigments selected from a first group consisting of low density pigments of smooth nodular shape having a maximum particle size of 325 microns and a second group consisting of pigments having a median particle diameter ranging from 0.5 to 20 microns and being shaped so that not more than 20% by weight of the smaller particles have ratios of any two dimensions exceeding 10. The total pigment volume concentration is not less than 40% and the total volume of both groups of pigments is not less than 75% of the total volume of pigments in the coating material. A blend of both groups contains from 20 to 95% by volume of the first group of pigments and from 5 to 80% by volume of the second group of pigments.
In U.S. Pat. No. 4,356,037 to Novak, an abrasion resistant coating is disclosed which includes a binder having dispersed therein first abrasion resistant particles of substantially uniform size and second abrasion resistant particles of substantially uniform size, the second particles having a diameter of less than 15.4% of the first particles. The use of two different sizes of abrasion resistant particles enhances the overall resistance of the coating to erosion by contact with various particle sized abrasives.
Although various types of fillers are disclosed for inclusion in base compositions for synthetic stucco, the final compositions are typically of substantial weight and do not achieve optimum application characteristics, particularly where trowel application of a decorative coating is required. Consequently, the search continues for synthetic stucco-type compositions which include fillers which reduce weight while increasing the ease of application.